Speaker
Description
Exciton-photon hybridization is commonly realized in geometrically defined cavities, where tuning typically requires modifying either the resonator or the excitonic medium. Here, we demonstrate experimentally that suspended subwavelength transition-metal-dichalcogenide (TMD) films support transition-radiation (TR) interference resonances that act as free-electron-defined photonic resonances and can be tuned continuously through the electron energy in cathodoluminescence (CL).
We first establish this mechanism in suspended dispersive films, where the measured CL spectra are well described by an analytical TR model and exhibit pronounced thickness- and electron-energy-dependent interference features. This identifies transition radiation in subwavelength films as an optical resonance set by the free electron rather than by a conventional cavity geometry. We then show that, in semiconducting TMDs, this resonance hybridizes with excitons. In WS2, both calculated and experimental CL spectra display exciton-induced spectral reshaping within the TR resonance, with thickness-dependent shifts consistent with detuning-controlled coupling to the A and B excitons.
Most importantly, by varying the electron energy from 10 to 30 keV, we continuously tune the TR resonance across the excitonic transitions and observe the exciton-photon detuning characteristic of hybridized states. These signatures are directly resolved in experimental cathodoluminescence spectra on thin suspended WS2 crystals.
Our results establish electron energy as a continuous external control parameter for exciton-photon coupling in suspended TMD films, without requiring any structural modification of the system. Free-electron-driven TR resonances therefore provide a nanoscale platform for studying and actively tuning hybrid light-matter interactions.
without structural modification and provides a free-electron-driven nanoscale platform for studying exciton-light interactions.